Who, What, Why: Does a reservoir need emptying if someone urinates in it?

Fisherman at Fewston Reservoir near Harrogate, Yorkshire

Some eight million gallons of treated drinking water have been flushed down the drain in the US state of Oregon after a man urinated into a reservoir. Did such a vast amount of water have to be dumped?

"Nobody wants to drink pee, and I don't want to deal with the 100 people who would be unhappy that I'm serving them pee in their water."

Those are the words of David Shaff, a water bureau official in Oregon's biggest city Portland, after flushing away 32 million litres of water.

They decided to take the drastic action after security cameras caught a 21-year-old man urinating into an uncovered reservoir. The water had already been purified and was to go directly to homes.

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Media captionJosh Seater says he felt "guilty" after urinating in the reservoir

But such a situation would never arise in the UK, for instance, because while most people think of reservoirs as outdoor lakes which are lovely to walk the dog around, all of the reservoirs containing treated water are covered.

While public health experts in the US said the urine in the reservoir was so diluted that it posed little health risk, the Oregon water chiefs did not want to take any chances. Plus, the cameras also showed something, as yet unidentified, being thrown into the water.

Toxicologist Prof Alan Boobis is "flabbergasted" by what he says is a complete overreaction.

"In a healthy person, urine is sterile. It's something we can say with confidence - it's not going to have any impact on anyone whatsoever."

He says even if chemicals were in the urine, they would not be in large enough quantities to cause damage.

"We are exposed to chemicals all the time but the intake is already below a level that's going to cause harm.

"Urine contains a whole range of substances that the body has no need for. It might contain chemicals that are potentially harmful but the levels are going to be very low when expelled by the body, and even lower when diluted by water."

Prof Boobis, from Imperial College London, points out that the reservoir already probably contained urine from fish and animals.

"The water was treated, so some bacterial agent was already killing things," he adds. "If someone urinates in a swimming pool, it doesn't become a problem, and that is a much smaller body of water."

Dr Paul Rumsby, from the Swindon-based Water Research Centre, says the US response was "very conservative" and "public acceptability" was probably more of a factor than science.

"It was probably that they thought the public would not accept it having realised what had happened."

He says if there had been a similar breach of security in the UK, a barrage of tests would have been carried out before dumping the water.

Thames Water, the UK's largest water and sewerage company, says all of its treated water reservoirs are covered to protect water quality, and the water is treated to stringent UK and European quality standards.

Sue Pennison, from the Drinking Water Inspectorate, says that since 1990, it has not been permitted in law for a treated water reservoir in the UK to be open to the elements.

"This is in order to protect supplies from contamination from many hazards, of which this example (human) is just one," she adds.

She says reservoirs containing treated water are emptied for inspection and cleaning every 10 to 15 years.

The human contaminator in the Oregon case said he had been drinking with friends and thought the reservoir was a sewage treatment plant.

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